The disclosure of Japanese Patent Application No. 2002-040679 filed on Feb. 18, 2002 including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a vehicle control apparatus having an idle stop function.
2. Description of Related Art
Conventionally, as is proposed, for example, in Japanese Patent Laid-Open Publication No. 2001-163071 and the like, there is a driving apparatus for a hybrid vehicle structured such that driving of a motor is directly connected to a crankshaft of an engine, and a driving force of the engine or the motor is transmitted to a driven wheel via an automatic transmission. In such a driving apparatus for the hybrid vehicle, a so-called idling stop system is provided which stops the engine while the vehicle is stopped, and restarts the engine at a time of starting.
For example, in the automatic transmission, a hydraulic control device is provided that hydraulically controls a friction engagement element for transmitting a driving force, and a mechanical oil pump is provided interlocking with the engine for supplying an oil pressure to the hydraulic control device. However, the engine is stopped when an idling stop as mentioned above is performed. Therefore, the mechanical oil pump stops and the oil pressure for engaging the friction engagement element is lost, creating a neutral state. Accordingly, for example, when restarting the engine and starting the supply of oil pressure from the mechanical oil pump, the engagement of the friction engagement element requires time, creating a time lag until the vehicle actually starts. Also, a shock is generated due to a sudden engagement of the friction engagement element. Therefore, it is necessary to increase the oil pressure supplied to the hydraulic control device by an electric oil pump that is driven independent of the driving of the engine, when the engine is stopped, namely, when the mechanical oil pump is stopped.
When attempting to supply an oil pressure by the electric pump that is identical to the oil pressure supplied by the mechanical oil pump in a state where the engine is driving, it is necessary to upsize the motor in the electric oil pump. However, this creates a problem with an increase in electric power consumption.
The invention thus provides a vehicle control apparatus that solves the above-mentioned problem by setting a standby pressure to less than a line pressure generated based upon the driving of the mechanical oil pump during idling and equal to or greater than a pressure by which a friction engagement element starts transmitting a torque.
The vehicle control apparatus according to a first exemplary aspect of the invention may be structured such that the controller controls the driving of the electric oil pump and generates the standby pressure supplied to the hydraulic servo of the friction engagement element based upon the driving state of the mechanical oil pump, and the standby pressure is set less than the line pressure generated based upon the driving of the mechanical oil pump during idling, and equal to or greater than the engagement starting pressure by which the friction engagement element starts transmitting the torque. Therefore, it is possible to set a low standby pressure supplied by the electric oil pump, thus allowing downsizing of the electric oil pump in addition to enabling a reduction in electric power consumption.
The vehicle control apparatus according to a second exemplary aspect of the invention may be structured such that the controller controls the driving of the electric oil pump and generates the standby pressure supplied to the hydraulic servo of the friction engagement element based upon the driving state of the mechanical oil pump, and the standby pressure is set less than the line pressure generated based upon the driving of the mechanical oil pump during idling, and equal to or greater than the stroke pressure which brings the piston and the friction plate into mutual contact without a gap. Therefore, it is possible to set a low standby pressure supplied by the electric oil pump, thus allowing downsizing of the electric oil pump in addition to enabling a reduction in electric power consumption.
For the purposes of this disclosure, device and means may be considered synonyms. Both relate to a computer and its programs and encompass any necessary memory. The device may be implemented solely by circuitry, e.g. hardware, or a combination of hardware and software. Further, in some cases, as defined in the specification, the device/means may include other elements.